Sound reproduction apparatus



Sept l2, 1967 G. E. OWEN. JR

SOUND REPRODUCTION APPARATUS 2 SheeJs-SheecA l Original Filed June l5, 1964 /n venor GEORGE E OWEN Jr FREQUENCY Sept l2, 1967 G. E. OWEN, JR

SOUND REPRODUCTION APPARATUS 2 Sheets-Sheet i3 Original Filed June l5, 1964 FIG. 3

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FREQUENCY United States Patent O M 2 Claims. (Cl. 181-31) This invention relates to sound reproduction apparatus, and more particularly to an improved speaker system. This application is a continuation of application Ser. No. 374,- 922, filed .lune l5, 1964, now abandoned.

Enclosures for audio signal speakers generally provide grill cloth or louvers to conceal the speakers and yet permit passage of sound freely therethrough. Such grill cloth or louvers may undesirably limit the cabinet designer in achieving an attractive overall cabinet design. This can be a particular problem in multi-speaker console record players wherein substantially the entire front of the cabinet may enclose speakers which radiate outwardly of the cabinet, thus generally requiring sound passage construction across the entire front wall of the cabinet.

With reference to more technical problems in speaker systems, it is noted that a combined speaker and enclosure will generally have a resonant frequency at the lower end of the audio frequency spectrum and may contri-bute to booming bass note sounds. Another problem with regard to low frequency speakers, or woofers, is that their response may extend well upwards into the higher frequencies. When used in a multi-channel system, irregular cross-over may result from this, and when used in a three channel stereophonic system, poor channel separation may result. Various other problems exist in connection with low frequency speaker systems such as Doppler effects created by the moving speaker cone, and distortion due to excessive speaker cone excursion.

It is an object of this invention to provide a speaker system having an enclosure which presents an attractive appearance while at the same time reducing or eliminating some of the foregoing technical problems.

Another object of the invention is to provide an improved -multi-channel speaker system.

Still another object of the invention is to provide a three-channel stereophonic sound reproduction system with superior channel separation and improved low frequency response.

A feature of the invention is the provision of a cabinet construction which mass loads a low frequency speaker to lower the natural resonance of the system.

Another feature of the invention is the provision, in a speaker system, of a soli-d panel over the front of a low frequency speaker with the top and bottom of the panel closed with the speaker enclosure so that the volume of air between the panel and the front of the speaker mass loads the speaker and the solid panel enhances the appearance of the assembly.

Still another feature of the invention is the provision of a compression enclosure over the front of a low frequency speaker in a stereo reproducing system, which enclosure is constructed to suppress high frequency signals from the speaker in order that only associated further speakers can produce these signals which contribute to stereo information.

In the drawings:

FIG. 1 is a perspective view of the front of a stereophonic phonograph cabinet constructed in accordance with the invention;

FIG. 2 is a front elevational view of the cabinet of FIG. 1;

Patented Sept. 12, 1967 ICC FIG. 3 is an enlarged sectional view taken along the line 3 3 of FIG. 2;

FIG. 4 is an enlarged sectional view taken along the line 4*4 of FIG. 2, with circuitry shown schematically;

FIG. 5 is a graph exhibiting the impedance characteristics of the system as compared to conventional systems; and

FIG. 6 is a graph exhibiting the response characteristics of the system as compared with conventional systems.

In accordance with the invention, a speaker system for reproducing three-channel stereophonic signals is enclosed in a cabinet. The cabinet has three aligned baille boards across the front, and high frequency speakers are disposed in each of the outside baille boards. A low frequency speaker is mounted in the center baille board, and a compression enclosure is secured to the cabinet over the low frequency speaker. The compression enclosure partially encloses a volume of air in front of the low frequency speaker to mass load the low frequency speaker and limit the high frequency response thereof. The resonant frequency of the low frequency Speaker system is thereby reduced to improve reproduction of lower frequency signals. Moreover, separation of the left and right stereophonic channels is improved while at the same time the overall appearance of the cabinet is enhanced.

Referring now more particularly to the drawings, FIGS. 1-4 illustrate one form of speaker system constructed in accordance with the invention. A cabinet having sides 11 and 12, top 13 and bottom 14, is supported on legs 15. The configuration of the supporting legs 15 may match the overall styling of the cabinet itself. The back of the cabinet is enclosed with an apertured panel 16 forming a substantially open backed cabinet as shown in FIG. 3 for ventilation and to permit free speaker cone movement.

The front portion of the cabinet includes a pair of baille boards 21 and 22 at either end thereof, extending from respective sides 12 and 11, to interior supporting panels 23 and 24. Batlle boards 21 and 22 provide support for a plurality of speakers 25 which carry the higher or `directional frequencies of the right and left channels of a stereophonic signal. The respective speakers 25 are driven by amplifiers 26 and 27 connected to a stereo signal source 28.

The lower frequencies of both the right and left channels of the stereo signal, which frequencies are non-directional in character, and therefore do not contribute to the stereophonic effect, are applied through a low frequency amplifier 31 to low frequency speaker 32. Low frequency speaker 32 could be a single large speaker as shown or a plurality of small speakers. Speaker 32 is mounted to a center baille board 33, which extends between supporting panels 23 and 24 and completes the front portion of the cabinet.

From an appearance standpoint, it is desirable that some form of decorative covering be placed over the speakers 25 in order that the speaker cones are not visible. Such `covering may take the form of grill cloth as is well known in the art, or may, as shown in the drawings, take the form of a plurality of vertical louvers 41. These louvers 41 have their lower ends mounted in respective right and left support rails 42 on a bottom panel 44, which bottom panel forms an extension of cabinet bottom 14. The top end of louvers 41 are supported by right and left support rails 45 similar to rails 42. Rails 45 are supported on an under panel 46 secured to the lower side of top 13. Louvers 41 are angularly disposed to conceal the speakers 25 and yet permit passage of sound therethrough.

A compression panel 51, which is substantially rectangular, is secured over the speaker 32. Panel 51 is solid, having no apertures, and has an outward surface which complements the overall cabinet design. The panel is more simple in decoration than the louvers, contributing to a Y Panels 51 and the top and bottom panels 46 and 44 form a compression chamber 58 to partially enclose a volume of air in front of low frequency speaker 32. This air mass loads speaker 32 by providing an effective reactance for the cone movement (i-n referring to an electrical equivalent of a mechanical system). This loading has the opposite reactive effect to what can be called stiffness loading. If the compression chamber S8 thus formed is closed too much, stiffness loading can result with an accompanying rise in the low frequency speaker system resonant point. However, by a proper amount of venting or opening of the sound passage around panel 51, the low frequency resonance can be established at an optimum low value. The piston action of the speaker cone forces the air out of the sides of the compression chamber 58 through the spaces between frame 52 of panel 51 and the innermost of louvers 41. This space, it should br: noted, is somewhat narrower than the distance between the outer face of the bafiie boar-d 33 and the inner face of the compression panel 51. Air is also forced out through the vent 55.

The natural resonance of the low frequency loudspeaker vibratory system is moved substantially lower because of this mass loading, as compared to no loading or stiffness loading referred to above. This lowering of the resonance frequency is also accompanied by an amplitude reduction in electrical impedance of the speaker system at and near the resonant frequency. These two factors are illustrated in FIG. .5 wherein the solid line 61 shows the impedance characteristics of the system when unloaded by the compression panel 55. The dotted line 62 shows the characteristics of the system with panel 51 in place. It will be seen that the resonant peak 62a, corresponding to the resonance peak 61a of curve 61, is wider and lower. Also at the high frequency end of the curves it will be noted that curve 62 increases substantially less than curve 61. The result is an overall lessening of the variation in impedance for the full audio frequency spectrum reproduced by speaker 32. Thus, over the useful part of this acoustic spectrum, the loudspeaker presents a more uniform electrical load upon the associated amplier 31. Therefore, more undistorted electrical audio power is available. The booming one note bass effect is substantially reduced, and the Doppler effect resulting from the moving cone is also reduced due to the loading of the air mass. Furthermore, there is less harmonic distortion because the excursion of the speaker cone is less for high peak outputs of the amplifier 31. This is also because of the damping effect of the air mass.

Referring to FIG. 6, a further effect of the improved system will be noted. The dark curve 71 represents the response characteristics of speaker 32 without panel 51 in place, and the dotted curve 72 represents the response characteristics of the system with panel 51 in place. It will be seen that as a result of the lowering and spreading out of the resonant frequency band due to pnael 51, the lower end of the response curve is shifted further to the left for improved low frequency reproduction.

It will also be noted from FIG. 6 that at higher frequencies the response curve of speaker 32, when mass loaded due to panel 51, takes a considerable drop. This insures that any directional frequencies reproduced by speaker 32 (which is positioned between the stereo speakers) will be at a sufiiciently low level as to not detract from the stereophonic effect. Greater improved stereophonic channel separation results. To further effect this separation, the inner surface of panel 51 may be lined with an acoustic damping material to absorb higher frequencies. This also minimizes or eliminates low frequency Doppler modulation from speakers radiating in an adjacent spectrum range. The radiation vent 55 may be positioned in such a manner relative to the vibratory system so that the acoustic phases radiated over certain parts of the spectrum are such that cancellation will be obtained, further aiding in spectrum balance adjustment.

It has been found that as a general rule, between one and four square inches of opening should be left for every twenty-five cubic inches of enclosed volume in compression chamber 58. In a system such as is shown, with the panel 51 spaced very colse to the speaker 32, between 25% and 50% of the peripheral area of the enclosed chamber should be left open. A satisfactory construction of the invention has been accomplished in accordance with the design shown in the drawings, wherein the distance between the inner surface of panel 51 and the outer surface of baffle board 33 was 1% inches, and wherein the compression panel 51, including frame 52, measured 18% inches high and 25 inches wide. The volume of air enclosed should be determined from the size of the speaker, but where a 15 inch speaker was used for speaker 32, the volume of the compression chamber 58 enclosed was approximately 820 cubic inches. The spaces 56 and S7 between the respective side edges of frame 52 and the innermost ones of louvers 41 was approximately l inch. Vent 55 was approximately inch by 16% inches. The total open area, therefore, was approximately 52 square inches.

It may therefore be seen that the invention provides an improved land attractive speaker systems effecting improved channel separation in stereophonic systems and improved low frequency response. Distortion is substantially reduced, and a better impedance match between the driving amplifiers and the speaker system is :also accomplished.

I claim:

1. A speaker system for increasing the low frequency response and improving stereophonic sound reproduction, including in combination, a cabinet having a baffle panel at the front thereof, said bafiie panel having a speaker opening therein, a low frequency speaker disposed adjacent said bafiie panel to emit sound through said opening thereof, a high frequency speaker disposed at each side of said low frequency speaker for reproducing stereophonic sound, said cabinet having an apertured back panel to permit free operation of said low frequency speaker, a solid compression panel having top, bottom and side edges and disposed in spaced relation from said baffle panel and in alignment with said low frequency speaker, means extending along the entire top edge of said panel to secure the same with respect to said baffle means, further means extending along the bottom edge of said compression panel to secure the same with respect to said baffle means, a portion of said cabinet extending in spaced relation along the side edges of said compression panel and spaced therefrom a distance less than the spacing between said compression panel and said baflie panel to define sound passages, the spacing Ibetween said baffle panel and said compression panel enclosing a volume of air to define a compression chamber, the compression chamber and the sound passages providing an effective loading of said low frequency speaker to increase the low frequency response thereof and decrease the high frequency response thereof so that said low frequency speaker emits reduced sound in the range of the high frequency speakers to improve stereophonic sound reproduction from said speaker systern.

2. The speaker system of claim 1 in which the area of the sound passages provides between one and four square inches of area for every 25 cubic inches of volume enclosed in said compression chamber.

References Cited UNITED STATES PATENTS 1,969,704 8/1934 DAlton 181-31 2,065,367 12/1936 Evans 181-31 Moore 181-31 De Boer 181-31 MacIntyre 312-7 Irby 181-31 Franke 179-1 Farwell 181-31 Taylor 1 8 1-3 1 STEPHEN I. TOMSKY, Primary Examiner. 

1. A SPEAKER SYSTEM FOR INCREASING THE LOW FREQUENCY RESPONSE AND IMPROVING STEREROPHONIC SOUND REPRODUCTION, INCLUDING IN COMBINATION, A CABINET HAVING A BAFFLE PANEL AT THE FRONT THEREOF, SAID BAFFLE PANEL HAVING A SPEAKER OPENING THEREIN, A FLOW FREQUENCY SPEAKER DISPOSED ADJACENT SAID BAFFLE PANEL TO EMIT SOUND THROUGH SAID OPENING THEREOF, A HIGH FREQUENCY SPEAKER DISPOSED AT EACH SIDE OF SAID LOW FREQUENCY SPEAKER FOR REPRODUCING STEREOPHONIC SOUND, SAID CABINET HAVING AN APERTURED BACK PANEL TO PERMIT FREE OPERATION OF SAID LOW FREQUENCY SPEAKER, A SOLID COMPRESSION PANEL HAVING TOP, BOTTOM AND SIDE EDGES AND DISPOSED IN SPACED RELATION FROM SAID BAFFLE PANEL AND IN ALIGNMENT WITH SAID LOW FREQUENCY SPEAKER, MEANS EXTENDING ALONG THE ENTIRE TOP EDGE OF SAID PANEL TO SECURE THE SAME WITH RESPECT TO SAID BAFFLE MEANS, FURTHER MEANS EXTENDING ALONG THE BOTTOM EDGE OF SAID COMPRESSION PANEL TO SECURE THE SAME WITH RESPECT TO SAID BAFFLE MEANS, A PORTION OF SAID CABINET EXTENDING IN SPACED RELATION ALONG THE SIDE EDGES OF SAID COMPRESSION PANEL AND SPACED THEREFROM A DISTANCE LESS THAN THE SPACING BETWEEN SAID COMPRESSION PANEL AND SAID BAFFLE PANEL TO DEFINE SOUND PASSAGE, THE SPACING BETWEEN SAID BAFFLE PANEL AND SAID COMPRESSION PANEL ENCLOSING A VOLUME OF AIR TO DEFINE A COMPRESSION CHAMBER, THE COMPRESSION CHAMBER AND THE SOUND PASSAGES PROVIDING AN EFFECTIVE LOADING OF SAID LOW FREQUENCY SPEAKER TO INCREASE THE LOW FREQUENCY RESPONSE 